1. Field of the Invention
The present invention relates to a method for evaluating a moving image resolution, and more particularly, to a method for quantitatively evaluating a moving image resolution for a display device.
2. Background of the Invention
In general, a liquid crystal display (LCD) device is being widely used due to advantages such as a light weight, a thin thickness, and low power consumption. Accordingly, the LCD device is being widely used to display images on screens of a portable computer such as a notebook PC, an office automation equipment, and an audio/video apparatus.
The LCD device displays desired images on a screen by controlling optical transmittance according to image signals applied to a plurality of controlling switching devices arranged in a matrix format.
The LCD device comprises an LC panel and a driving portion. The LC panel includes an upper substrate, a color filter substrate facing a lower substrate, a thin film transistor (TFT) array substrate, and an LC layer disposed between the upper and lower substrates. The driving portion drives the LC panel by supplying scan signals and image information to the LC panel.
Have been proposed various methods for evaluating a moving image resolution for the LCD device. Representative methods include a direct evaluation method by an inspector's naked eyes while displaying a test pattern on a screen and moving the test pattern in a predetermined direction, and an indirect evaluation method by using a short time Fourier transform. According to the indirect evaluation method, an image of a test pattern is obtained while displaying the test pattern on a screen and moving the test pattern in a predetermined direction, and then a result of the image having undergone a short time Fourier transform is analyzed.
Hereinafter, the conventional method for evaluating a moving image resolution will be explained in more detail with reference to FIGS. 1 to 3.
FIG. 1 is a view showing a test pattern displayed on a screen of an LCD device in the conventional method for evaluating a moving image resolution, and FIG. 2 is a view showing images of the test pattern of FIG. 1, the images directly observed by an inspector's eyes while the inspector moves the test pattern in the arrow direction.
Referring to FIGS. 1 and 2, in the direct evaluation method by an inspector's naked eyes, a test pattern is displayed on a screen for a display device. Then, the inspector directly observes images of the test pattern while moving the test pattern in the arrow direction. Here, if lines having the same number as that of the test pattern are observed, it is judged that the display device has successfully undergone a moving image resolution test (OK). However, if the number of observed lines is different from the number of lines of the test pattern, it is judged that the display device has unsuccessfully undergone a moving image resolution test (NG).
FIG. 3 is a view showing a method for evaluating a moving image resolution by a short time Fourier transform, in which FIG. 3A shows an image of a test pattern displayed on a screen, the image observed while the test pattern is moved in the arrow direction, FIG. 3B is a graph showing a brightness level corresponding to any horizontal line of the image, and FIG. 3C is a graph sequentially showing a position, an amplitude, and a phase according to a frequency with a result obtained by applying a short time Fourier transform to the brightness level.
As shown in FIG. 3A, a test pattern is displayed on a screen. Then, as shown in FIG. 3B, a bright level graph of the test pattern corresponding to any horizontal line is obtained while moving the test pattern in the arrow direction. Then, as shown in FIG. 3C, results to which a short time Fourier transform has been applied are analyzed, thereby judging whether the display device has successfully undergone a moving image resolution test or not.
However, the conventional method for evaluating a moving image resolution has the following problems.
Firstly, in the method by an inspector's naked eyes, different test results may occur due to a difference between inspectors. This may cause a difficulty in quantifying tested results with respect to images of a test pattern.
Secondly, in the method by a short time Fourier transform, it is difficult to quantify test results obtained by applying a short time Fourier transform due to irregularity of the results.